1. Field of the Invention
The present invention relates to an image capturing system, and more particularly to a medical imaging system achieving a smaller volume and higher luminous efficiency.
2. Description of the Prior Art
Image capturing technology, particularly that for a biological cavity, is required to have an adequate external illumination that can pass through the opening of the cavity to provide illuminating light with sufficient luminance, for there is no light source illuminating the interior of the biological cavity and the opening of the biological cavity is often relatively small, so that the imaging system may capture reflected image forming light to render a clear and accurate image within the cavity for observation or filming.
A prior art illuminating system employed a ring-shaped hollow reflective mirror to reflect light rays of a light source in coordination with a lens set to direct illuminating light into an opening of a cavity. The image light passed through the hollow region of the ring-shaped hollow reflective mirror to form an image. However, normally the luminous intensity distribution of a light source is a Lambertian distribution or Gaussian distribution that has higher intensities in the central region. The ring-shaped hallow reflective mirror was unable to utilize this central portion of the light to provide illumination, thereby causing a low luminous efficiency.
Another prior art illuminating system used a point light source with a reflective mirror and lens set to focus illuminating light at an opening of a cavity, and then captured image forming light from the cavity with an image forming system off axially disposed with respect to the illuminating system to form an image. Although the problem of low luminous efficiency was solved, the off-axis configuration of the illuminating system and the imaging system required more optical components, and raised the manufacturing cost. Besides, the volume and length of the system were also increased, which limited the field of view of the system, and hindered the design of a large field of view and large aperture system. As a result, the illuminating view and the imaging view were different, lowering the capturing accuracy.
In summary, it is highly desirable to provide a system with a reduced volume and higher luminous efficiency.